1. Field of the Invention
The present invention relates generally to fiber optic telecommunication. More particularly, the present invention pertains to a system and method for simple, rapid detection of an optical fault within the optical domain in a communication network.
2. Related Art
A communication network serves to transport information among a number of locations. The information to be transported is often presented to the network in the form of time-domain electrical signals representing a combination of telephony, video, or computer data in a variety of formats. A typical communication network has many physical sites called nodes interconnected by information conduits called links. Each link carries data from one node to another node. Each node can contain equipment for combining, separating, transforming, conditioning, and routing data.
Optical fibers are increasingly relied upon for carrying vital communications traffic. Fiber trunks extend between nodes (i.e. cities) forming networks extending across states, nations, and continents. Fiber cables whether laid out above ground, underground, or underwater are subject to damage. For example, lightning, backhoes, fires, train derailment, trawler nets, and shark attacks have been reported to have severed or impaired optical fiber connectivity. See, Grover, Wayne PhD., "Distributed Restoration of the Transport Network," Network Management into the 21st Century, Chapter 11, IEEE Press, (1991), p 337.
Fiber optic cables carry far greater amounts of digital data than conventional electrical cables. A single fiber operating at approximately 10 Gb/s and packeting data according to a standard SONET OC-192 protocol, carries data equivalent to over 128,000 voice calls. Moreover, dozens of fibers may be included in a single cable. The impact of a cable cut, or even a single optical fiber failure, can be widespread. Sudden link failure due to a fiber failure, cable cut, nodal failure, or any other system error can cause a significant loss in revenue for a network owner or network subscriber.
Sophisticated consumers no longer tolerate disruptions of service. Prompt detection of optical signal impairment or loss is therefore essential to effective network management. Conventional restoration systems detect loss of fiber connectivity in the electrical domain. For example, the absence of a traffic signal at a light terminal element (LTE) receiver is detected. Detecting signal loss at the LTE can take two or more seconds--too slow for modern industry demands.
All-optical networks often include endpoint nodes optically interconnected through paths which include intermediate optical switching nodes. Each path can include multiple intermediate nodes coupled to one another through multiple spans or links. Detecting signal loss at an LTE located at an endpoint node, however, only provides a fault indication for the entire path between endpoint nodes. The specific intermediate span or link which is the source of the fault indication cannot be distinguished.
Moreover, implementing additional detection circuitry in the electrical domain can be costly. At a practical level, some existing LTE circuits cannot be easily accessed or re-configured to accommodate fiber fault detection processing.
What is needed is a simple, fast method and system for detecting optical faults in the optical domain of a fiber optic network.